1. Field of the Invention
The present invention relates to processes for reinforcing or stiffening extruded metals, composites or plastics during the extrusion process and to the resulting products. The process particularly refers to processes and products with pre-stressed reinforcement within the extruded article.
2. Background of the Invention
The extrusion process is an economical way to provide complex shape profiles along the length or axis of an elongated article or material. Extrusion may generally be performed on any material that can exhibit plastic or fluid flow under high pressure. Many structural elements can be provided by extrusion of metals, alloys, composites and polymeric materials. Among the most commonly extruded structural materials are metals (especially aluminum, although steel, manganese, magnesium, titanium, lead, copper, nickel and other metals may be used); alloys such as brass; nitinol, zirconel, niconel; polymeric materials; inorganic oxides (e.g., silica, zirconia, titania, and the like); composites (e.g., mixtures of materials in various physical forms such as particulates, platelets, fibers, and filaments, with such materials comprising polymers, metals, inorganics (e.g., inorganic oxides, inorganic sulfides, inorganic nitrides or carbonates, etc.); ceramics; and glass are some other materials that work well in this process.
The concept of extrusion is well understood. A billet or slug of the material to be extruded is positioned in the extrusion press in front of a movable ram or piston, e.g., a hydraulically operated ram or piston and the billet is sealed in by the diehead assembly. An exit end, opposite the ram, contains a die with an opening having the profile which is desired in the extrusion's cross section. The ram is moved toward the diehead with tremendous force. This force has to be sufficient to convert solid material that is to be extruded into a plastic or liquid state which will allow the extruded material to flow through the diehead while it is being pressed by the ram. As the flow of material is forced through the die, it tends to conform to the shape of the cutout or opening in the die, producing an extruded product with a cross-section which matches the shape of the opening in the die. As the extrudate comes out of the diehead, it is cooled (usually with water) to harden the extrudate into the shaped article intended from the process. To produce a tubular shape, another die (called a bridge die) is positioned near the end of the die (near the opening) so that the flow of the extrudate also flows over the bridge die, which in combination with the primary die, forms a shape or cross-section including and opening. The bridge die is used to shape the final flow pattern of the extrudate by filling up part of the center of the flow, thus not allowing material to flow in the blocked area. The bridge die is attached to the die head and positioned in the flow path of the billet.
Common shapes for extruded products are dependent upon the structural, thermal and trim shapes that are desired in their end use. Trim pieces for the automobile industry, for example, may have any non-traditional cross-section selected for the sake of appearance. Since a primary use of extruded products is to provide structural strength or stiffness, structural shapes like angles, channels and tubing will be primarily considered in the discussion of this technology, even though they are being used as examples where more decorative shapes and sizes may equally benefit. When an extruded product is designed, the engineer primarily uses the mass of the extrusion to calculate the strength of the final product. The engineer will attempt to put the maximum surface area of the product in the plane of deflection to aid in stiffening the material. Although some shaping of the product (as with an I-beam) can be used to affect the strength of the extruded product with respect to a given weight of material in the extruded product, to handle more weight, the engineer typically uses more material. When space is at a premium, the originally selected material may not work and would have to be replaced by a stronger material. The extrusion process is thus economical, but it is limiting in the area of material selection for stiffness applications.
A current method of design for transportation industry equipment such as semi truck trailers is to use as much material as necessary to support the load, always providing the design with a safety factor. Unfortunately, this method dictates the size of the trailer because ground based transportation has load and size restrictions. The materials used to build semi trucks and trailers are significant limiting factors with respect to size and weight of the final product.
Because fabricated components built from extruded materials are sometime subject to rapid acceleration and deceleration, the methods used to join two pieces in an assembly are critical with respect to the final product staying tight and rigid after final construction. When one piece is joined to another and the composite piece is subject to motion or stress, the joint itself could loosen or fail. The assembly must be able to withstand this motion or stress to prevent failure of the final product at the juncture of the two pieces. The materials used must be of sufficient size to overcome this possible motion or stress, and a limiting factor is that the material is not stiff enough for some applications.
Because of the costs associated with the mining, smelting and shaping the aluminum it is prudent to use the material strength and stiffness available per pound for the application or load.
As noted above extrusions have disadvantages and limitations. There is a need for an extrusion that minimizes some of these limitations. There is a need for aluminum that maximizes the stiffness in an extrusion. There is a need for an extruded product (or alternatively referred to as an extrusion) that has higher tensile strengths relative to physical size. There is a need for standard structural shapes to withstand more vibration. There is also a need for an extruded product that has a very high strength to weight ratio.
The addition of reinforcements into molded and/or extruded articles has been practiced in the past to provide additional strength to articles. U.S. Pat. No. 4,005,255 describes a composite section with a body comprising light metal (such as aluminum alloy) having a number of inserts, including particular inserts therein of a metal of higher strength than the light metal of the body. The inserts are improved by not being round (which might slip too easily through the matrix of the body), and the novel shape of the inserts acting to engage the insert to the matrix. The inserts are fed into the side of the extrusion die and passed through channels so that the inserts are surrounded by and bonded to the light metal.
U.S. Pat. No. 4,030,334 describes an apparatus and process for providing inserts into extruded composites, especially where the matrix is light metal, by feeding the inserts into the matrix while it is being extruded. The matrix flows while the insert remains substantially unchanged in its physical form. Bonding between the insert and the matrix may be mechanical, metallurgical or both.
U.S. Pat. No. 2,778,059 shows the formation of insulated multiconductor wire by feeding multiple filaments of wire through an extrusion head, where plastic is extruded over the wires. The wire appears to be advanced through the extrusion head by being pulled by a capstan driven by a motor. It appears that the capstan acts to position the reinforcement and is not intended to nor inherently does provide significant elongation and strength by stretching a reinforcing element.
U.S. Pat. No. 3,137,389 describes an extrusion cladding process in which a billet of metal, such as aluminum, is extruded over a moving core of metal to weld the cladding to the core metal without deforming the core.
U.S. Pat. No. 2,741,363 describes a method and resulting composite article with a defined cross section, including extruded aluminum bodies with embedded reinforcing wires. Reinforcing wires are drawn through a mandrel after entering the extrusion zone through bores. Wire guiding elements have surfaces which lie in planes that converge towards each other (as with a funnel). The wires are prevented from being moved out of their desired placement by the forces placed on the ends of the wire by a wire guiding body.
U.S. Pat. No. 3,399,557 describes a method and apparatus for extruding soft metal sheathing onto a hard metal wire. The clad wire is susceptible to drawing after the sheath (e.g., aluminum) has been bonded to the core.
U.K. Patent No. 1 482 205 describes an improved extrusion method for reinforcing a main matrix with reinforcing elements such as wires or rods. Aluminum matrices are reinforced by cylindrical steel reinforcing wires. A deflector member may be used to generate a void to insure intimate contact between the core element and the matrix metal upstream of the die exit plane. The matrix material is described as exerting a functional drag on the core to draw the core element through the die orifice.
U.S. Pat. No. 3,706,216 describes a method for reinforcing extruded articles comprising pulling a wire through a die while pressure is applied to an extrudate. The extrudable materials include polymers and metals (including aluminum, magnesium, titanium and steel). The simultaneous steps of pulling on the wire and pushing on the extrudate causes the extrudant to encircle the wire to produce a coated wire.